Powdery mildew (PM) is one of the most serious global diseases of cucurbit, apple, rose, grape and cereal crops. The ubiquitous disease creates considerable problems because it reduces the photosynthetic area of leaves, which in turn diminishes yield (50-100% in the absence of control) and product quality.
Worldwide costs associated with this disease are estimated by Dow AgroSciences to exceed US$100 million. Serious limitations with existing controls, namely DMI (demethylation-inhibiting) fungicide resistance, restrictions on the use of sulphur and sodium bicarbonate in organic systems, the lack of eradicant activity, and the lack efficacious organic alternatives, drive the need to find new control alternatives.
Brazilian (1) and Australian (2) researchers have reported that milk is as effective as conventional fungicides in the control of PM in squash and grape crops respectively. While the Brazilian research was conducted using fresh whole-milk, the Australians have reported that full-fat and skim milk powders, and whey and whey protein powders are effective. Neither group of researchers have reported the compound(s) responsible for the fungicidal activity or the mode of action. A wide range of milk components including salts, proteins, fats, calcium, and free radicals, are postulated to contribute to antifungal activity and/or stimulate biological control.
Fatty acids are reported to be toxic to diverse fungi and bacteria (3-5). The anti-fungal activity of plant oils (olive oil, canola oil, corn oil, grape seed oil, peanut oil, safflower oil, soya bean oil and sunflower oil) and mineral oils (JMS stylet oil) against powdery mildew has been reported (6-8).
Problems associated with using whole- or skim-milk products as fungicides include milk spoilage, development of unpleasant odours, handling difficulties, application problems, poor durability of control, and unwanted growth of other non-target organisms, e.g. sooty mould. Fungicides containing free fatty acids and/or plant or animal oils/fats can be expensive, clog agricultural spray equipment, provide only variable disease control, have phyto-toxic effects and may be restricted products in organic systems.
It is therefore an object of the invention to provide a fungicide that overcomes or ameliorates one or more of the problems with prior art fungicides, or that at least provides the public with a useful choice.